Newly released documents stoked a high-powered standoff Tuesday over whether the operator of the San Onofre Nuclear Generating Station may have skirted the appropriate review of replacement steam generators that have sidelined the plant, and whether a restart can occur without trial-like public hearings.

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Sen. Barbara Boxer, D-Calif., called on the Justice Department, along with state and federal regulators, to review whether the Rosemead-based utility misled nuclear safety officials about the extent of design changes in order to avoid a more rigorous regulatory review — forwarding correspondence by Edison dating back nearly to the outset of the equipment project.

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“It makes me very concerned that there is misconduct here,” said Boxer, chairman of the Senate environment and public works committee that provides oversight of the Nuclear Regulatory Commission. “I will leave that to the Justice Department.”

Two letters from Edison, dating from November 2004 and June 2005, raised eerily prescient concerns about design challenges. Edison Vice President Dwight Nunn, who left the company in 2005, warned of the potential for dry, fast steam conditions within the generators and difficulties with anti-vibration braces that have been linked to the rapid degradation of generator tubes carrying radioactive water.

San Onofre has been offline since a radiation release and tube leak set off alarms at the plant on Jan. 31, 2012.

Steam generators are routinely replaced at aging nuclear plants without major changes to plant safety specifications, but nuclear safety groups believe changes to San Onofre’s generators were so extensive as to require a major amendment to the plant’s operating rules.

In the letters addressed to generator manufacturer Mitsubishi Heavy Industries, Nunn acknowledged that “although the old and new steam generators will be similar in many respects, they aren’t like-for-like replacements.” That drew Boxer’s attention.

“My concern is that the SoCal Edison people told regulators one thing and did another,” Boxer told reporters in a news conference by telephone from California. “They self-certify that this would be a like-for-like replacement. And in this letter you see they said it was not a like-for-like replacement. That’s misleading people. That’s a way to avoid the full license review.

“I don’t have confidence in Southern California Edison, given what I now know.”

Edison, in a written statement, said the letters demonstrate its vigorous oversight of Mitsubishi’s work before designs were completed.

The utility said the new generator design met the criteria for prior approval without a major license amendment. That evaluation was conducted by Edison and reviewed by the NRC.

“At no time did Edison hide the differences from the NRC, nor did it seek to mislead the NRC,” the statement said. “Any suggestion that seeks to draw from the November 2004 letter the contrary conclusion is simply incorrect.”

The very purpose of the regulations in question, Edison said, is to permit certain types of design changes with prior approval of the nuclear commission.

Nuclear commission spokesman Victor Dricks said the agency is not commenting on the letters. Mitsubishi said it was evaluating the letters.